Most vehicles are equipped with a brake system for retarding or stopping movement of the vehicle in a controlled manner. A typical brake system for an automobile or light truck includes a disc brake assembly for each of the front wheels and either a drum brake assembly or a disc brake assembly for each of the rear wheels. The brake assemblies are typically actuated by hydraulic or pneumatic pressure generated when an operator of the vehicle depresses a brake pedal. The structures of these drum brake assemblies and disc brake assemblies, as well as the actuators therefore are well known in the art.
A typical disc brake assembly, such as disclosed in U.S. Pat. No. 6,533,079, includes an anchor bracket or similar carrier which is secured to a fixed, non-rotatable component of the vehicle. A pair of brake pads are supported by a caliper on the anchor bracket for sliding movement relative to the anchor bracket. The brake pads have respective friction surfaces which are disposed on opposite sides of a brake rotor. The rotor, in turn, is connected to and rotatable with the wheel of the vehicle. To effect braking action, the brake pads are moved inwardly toward one another so as to frictionally engage the opposed sides of the brake rotor. Such frictional engagement causes retarding or stopping of the rotational movement of the brake rotor and, therefore, the wheel of the vehicle in a controlled manner.
The caliper selectively moves the friction pads into frictional engagement with the brake rotor through guide pins or other components that are slidably supported in the caliper housing relative to the fixed anchor bracket. The caliper housing is generally C-shaped, having an inboard leg adjacent the inboard brake pad and an outboard leg adjacent the outboard brake pad. One or more hydraulically or pneumatically actuated brake pistons are provided in respective cylindrical recesses. Early caliper brakes employed pistons in both the inboard and outboard portions of the caliper to actuate inboard and outboard brake pads respectively. More recently one or more pistons are located to one side of the disc, typically in the inboard leg of the caliper adjacent to the inboard brake pad. In these more recent arrangements, when the brake pedal is depressed, the piston and the inboard leg of the caliper are urged apart from one another so that the piston and inboard friction pad are urged axially outwardly, while the outboard leg of the caliper and outboard friction pad are urged inwardly. The piston is disposed adjacent to the inboard brake pad and, therefore, urges it outwardly toward the inner side of the rotor. Because the caliper is slidably mounted on the pins of the anchor bracket, the outboard leg of the caliper and outboard brake pad are urged inwardly toward the outer side of the rotor and as a result, the brake pads frictionally engage the opposed sides of the rotor. The pins may be fixed to the anchor bracket and slidably engage bores in the caliper, or the pins may be fixed to the caliper and slidably engage bores in the anchor bracket.
In order to reliably obtain the braking force from the disc brake system having the slide pin type guide, the slide pin should smoothly slide in the guide hole in the direction perpendicular to the disc. Variations in the size and location tolerances within the brake system detract from the desirable operation. Smoother operation may be achieved by employing a bushing of proper lubricity between the pin and hole. For example, U.S. Pat. Nos. 4,331,221 and 6,810,122 disclose bushing of electrometric material that form a portion of the bore in which a guide pin moves while damping bushing is shown in U.S. Pat. No. 4,753,326. All of these bushing arrangements are standardized, that is, are not designed and sized to fit a particular pin and bore. None of these bushings reduce tolerance variations among various pins and bores and none provide a proper minimal running clearance between the pin and bore and are not formed in situ, rather, they are all fabricated and later adapted to fit a particular pin/bore combination. Thus, it is desirable to minimize the cumulative effects of size and tolerance stack-up in a ZOH style caliper and anchor bracket assembly.